On Thu, Dec 14, 2017 at 1:08 PM, Al Viro <[email protected]> wrote: > On Thu, Dec 14, 2017 at 12:17:57PM -0800, Cong Wang wrote: >> syzbot reported we have a use-after-free when mqueue_evict_inode() >> is called on __cleanup_mnt() path, where the ipc ns is already >> freed by the previous exit_task_namespaces(). We can just move >> it after after exit_task_work() to avoid this use-after-free. > > What's to prevent somebody else holding a reference to the same > inode past the exit(2)? IOW, I don't believe that this is fixing > anything - in the best case, your patch papers over a specific > reproducer.
You are right, I missed mq_clear_sbinfo(). And the offending commit is: commit 9c583773d036336176e9e50441890659bc4eeae8 Author: Giuseppe Scrivano <[email protected]> Date: Fri Dec 15 01:06:28 2017 +0000 ipc, mqueue: lazy call kern_mount_data in new namespaces kern_mount_data is a relatively expensive operation when creating a new IPC namespace, so delay the mount until its first usage when not creating the the global namespace. This is a net saving for new IPC namespaces that don't use mq_open(). In this case there won't be any kern_mount_data() cost at all. On my machine, the time for creating 1000 new IPC namespaces dropped from ~8s to ~2s. Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Giuseppe Scrivano <[email protected]> Cc: Manfred Spraul <[email protected]> Cc: Davidlohr Bueso <[email protected]> Cc: Al Viro <[email protected]> Signed-off-by: Andrew Morton <[email protected]>
